Grime's CSR theory revisited: A whole-plant view of vascular plant functioning across contrasting environments

To understand how plants adapt to environmental conditions within the constraints of trait trade-offs, Grime proposed the competitor, stress-tolerator and ruderal (CSR) ecological strategy theory. This framework categorizes species based on their responses to two key environmental factors: disturbance and stress. Despite its widespread use in ecological research, CSR theory has not yet been rigorously validated against species-specific environmental preferences, particularly for species beyond Great Britain. Additionally, the typical characteristics of these strategies, particularly in relation to root and flower traits, remain poorly understood. We analysed a dataset of 7037 vascular plant species to investigate the relationships between CSR strategies (quantified using the ‘StrateFy’ tool) and environmental preferences, as well as their associations with 31 plant traits, encompassing above-ground vegetative, below-ground and reproductive traits, using canonical correspondence analyses. Furthermore, we explored the potential cascading links among environmental preferences, CSR strategies and functional traits using correlation analyses. Our results revealed that CSR strategies, as reflected in CSR scores, are strongly correlated with species' environmental preferences for both stress and disturbance, and support Grime's hypothesis across a broad range of species and environmental conditions. Moreover, CSR strategies exhibit robust correlations with plant traits from roots to shoots. Specifically, C-selected species, which thrive in stable, nutrient-rich environments, are characterized by large seeds and bud banks; S-selected species often grow in light-rich environments and tolerate grazing, possess thicker leaves and often exhibit self-compatibility. In contrast, R-selected species, which dominate in highly disturbed, nutrient-rich habitats, form dense seed banks to maximize regeneration potential. Synthesis. Our findings provide strong empirical validation of the CSR theory using an extensive species dataset and expand the number and types of traits that are significantly associated with the CSR axes. This study highlights the broad applicability of the CSR theory for understanding plant adaptation and ecological functioning, making it a valuable tool for research in community assembly, functional trait diversity and evolutionary ecology, particularly in the context of climate change and increasing human-induced disturbances.